Re: [PATCH] sched/fair: Optimize sum computation with a lookup table

From	Juri Lelli <juri.lelli@arm.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] sched/fair: Optimize sum computation with a lookup table
Date	2016-04-08 18:30 +0200
Message-ID	<rlHse-6Dc-5@gated-at.bofh.it> (permalink)
References	<rlBmP-1PG-41@gated-at.bofh.it> <rlBZw-2oe-3@gated-at.bofh.it> <rlCiS-2wH-7@gated-at.bofh.it>
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Hi,

On 08/04/16 12:54, Peter Zijlstra wrote:
> On Fri, Apr 08, 2016 at 03:31:41AM -0700, Joe Perches wrote:
> > On Fri, 2016-04-08 at 10:07 +0800, Yuyang Du wrote:
> > > __compute_runnable_contrib() uses a loop to compute sum, whereas a
> > > table lookup can do it faster in a constant time.
> > 
> > Perhaps this becomes rather fragile code overly dependent on the
> > current #define values of LOAD_AVG_MAX_N and LOAD_AVG_PERIOD.
> 
> Too late for that, these tables already heavily depend on these values.
> 
> Commit 5b51f2f80b3b ("sched: Make __update_entity_runnable_avg() fast"),
> which introduced these tables, includes a program to re-compute the
> values if we ever need to change them.
> 
> It might maybe make sense for Yuyang to update that program to also
> compute this new table and include the whole new program in the
> Changelog of this patch.
> 

+1 on this. That program turns out to be really useful if one needs to
recompute tables.

Best,

- Juri

Thread

[PATCH] sched/fair: Optimize sum computation with a lookup table Yuyang Du <yuyang.du@intel.com> - 2016-04-08 12:00 +0200
  Re: [PATCH] sched/fair: Optimize sum computation with a lookup table Joe Perches <joe@perches.com> - 2016-04-08 12:40 +0200
    Re: [PATCH] sched/fair: Optimize sum computation with a lookup table Peter Zijlstra <peterz@infradead.org> - 2016-04-08 13:00 +0200
      Re: [PATCH] sched/fair: Optimize sum computation with a lookup table Juri Lelli <juri.lelli@arm.com> - 2016-04-08 18:30 +0200
  Re: [PATCH] sched/fair: Optimize sum computation with a lookup table Peter Zijlstra <peterz@infradead.org> - 2016-04-08 12:50 +0200
  Re: [PATCH] sched/fair: Optimize sum computation with a lookup table Peter Zijlstra <peterz@infradead.org> - 2016-04-08 12:50 +0200
  Re: [PATCH] sched/fair: Optimize sum computation with a lookup table Morten Rasmussen <morten.rasmussen@arm.com> - 2016-04-08 13:30 +0200

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